This invention is related to an apparatus and method for releaseably joining elements and, in particular, to an apparatus and method for releaseably joining elements with a clampband that is capable of releasing the elements without damaging the elements by reducing, if not eliminating, the release of constrained energy by the clampband that normally results in shock to the elements when the elements are released.
It is sometimes necessary to join various elements, at least temporarily, by clampbands. A clampband is generally made of one or more interconnected segments separated by respective openings. Typically, a connector, such as a bolt, extends across each opening in the clampband to allow the clampband to be tightened or loosened around the joined elements. The connector that extends across a respective opening may have various forms depending upon the application of the clampband. A commonly used clampband in the aerospace industry is referred to as a Marmon-type clampband.
To join elements, a clampband is placed around the abutting end portions of the elements and the clampband is tightened to exert enough tension to hold the elements together under the forces to which the elements are subjected. Typically, a respective fitting is mounted to the end portion of at least one element. Thus, the clampband can extend around and engage the fitting(s) so as to securely join the elements when subjected to the anticipated forces. The forces include, for instance, the weight of the elements and the forces exerted on the elements during their movement. For example, the clampband around the fitting must be tight enough to prevent the forces acting on the elements during movement from detaching the elements. In the aerospace industry, for instance, the elements joined by a clampband are generally heavy and subject to significant forces during movement, particularly during the take-off or launch. Specifically, a satellite launch vehicle, which is joined to a satellite by a clampband, is capable of lifting 2,000 to 31,000 pounds. In addition, the satellite and the launch vehicle are subject to significant forces during the launch process due to high inertial loads and acceleration of thrust. Thus, the connector that extends across the opening in the clampband utilized in satellite applications must tighten the clampband around the satellite and the launch vehicle to the extent necessary to securely join the elements and withstand the substantial forces acting thereupon.
In certain applications, clampbands are designed such that they may release the elements at a chosen time. The clampband release procedure may be manual or automated. To release the elements held by the clampband, the clampband must be loosened and/or opened in some manner. Typically, loosening and/or opening the clampband involves lengthening or detaching the connector that extends across the opening in the clampband. In the aerospace industry, for example, clampbands may be used to temporarily join launch vehicles to payloads, such that the launch vehicle may separate from the payload once it completes its function. Specifically, during the launch of a satellite, a clampband joins the satellite to the launch vehicle and once the launch vehicle transports the satellite to the desired location for orbit, the launch vehicle must separate from the satellite.
One conventional clampband separation method is to cut the connector that extends across an opening in the clampband. Typically, the clampband includes an automated cutter that is attached to a clampband segment, such that the connector may be cut and the clampband opened at a chosen time. At the time the connector is cut, the sudden release of constrained or potential energy stored in the clampband creates a low frequency shock in the elements due to the structural vibrations at the natural frequencies of elements. The tighter the clampband is applied to the fitting(s) between the elements, the higher the tension that is exerted by the clampband upon the fitting(s), and the larger release of constrained energy and corresponding shock experienced by the elements upon clampband separation. Thus, elements that are heavy and/or that are subject to significant forces during movement, which must be held together temporarily by a clampband, experience a large shock upon clampband separation because of the significant amount of constrained energy that is released when the tightened clampband is separated.
Another technique for releaseably joining elements includes a separation joint that engages the elements and that includes a tube capable of being reshaped in order to release the elements. The joint is connected to both elements in order to hold the elements together. The joint generally includes a pair of members that are brought together from opposite sides of the elements to secure the elements therebetween. The joint also includes a reshapable tube positioned between the joint members. The reshapable tube is initially substantially oval-shaped to permit the joint members to be brought together in order to secure the elements. The joint also includes a linear explosive assembly within the tube. In order to release the elements, the linear explosive assembly is detonated. This detonation creates pressure within the tube, which causes the tube to become substantially round. As the tube becomes round, it forces the joint members on either side of the tube to separate, which permits release of the elements. This technique, however, also creates a release of constrained energy when the tube causes the joint to break, which causes the elements to experience shock similar to that described above. In addition, this technique does not utilize the conventional clampband assembly, such that the joint may require more time and labor for installation than the conventional clampband assembly, which is typically readily available and utilizes known procedures for installation.
If the elements include or contain equipment that is sensitive to sudden movement, then the shock created upon clampband separation or joint breakage may damage the equipment, particularly if the clampband is tightly attached to the fitting(s) between the elements. The shock created upon clampband separation or joint breakage due to the release of constrained energy is particularly problematic for satellites, which contain highly sensitive sensors and antennas, in addition to other precision equipment. The shock may damage the sensitive and expensive electronics of the satellite, which may decrease the effectiveness of the satellite or render the satellite useless. In addition, in order to prevent the equipment from being damaged due to the clampband separation or joint breakage shock, the equipment must include protection, such as shock absorption means and the like, which increases the cost of the equipment.
The conventional low shock clampband separation techniques include provisions to attempt to mitigate the shock produced by conventional clampband separation techniques. One example of an attempt to mitigate the shock includes providing a slower manner of separating the conventional clampband. For example, instead of cutting a connector that extends across an opening in the clampband, a nut that holds the connector in the clampband may be rapidly spun off of the connector in order to open the clampband. An example of this type of clampband is commercially available from Saab-Ericsson Space AB. In the case of the Saab-Ericsson low shock clampband, this technique takes approximately four milliseconds, instead of the less than one millisecond that is required to cut the connector with a standard bolt cutter. Thus, the nut spinning technique reduces the shock experienced by the elements when the clampband is opened, but it still has significant shock content between 1,000 and 10,000 Hertz. In order to prevent damage to and reduce the risk of unexpected failure of sensitive equipment, the shock levels to the elements should be less than 100 g's between 1,000 and 10,000 Hertz. In addition, when the shock levels are less than 100 g's between 1,000 and 10,000 Hertz, the risk of failure of less expensive, off-the-shelf type components is reduced, and therefore may be used in the elements that are held together by the clampband, instead of costly components with significant amounts of built in protection to withstand larger shock levels. As such, even with the nut spinning clampband separation technique, an expensive protection means for the equipment is still required.
Thus, there exists a need in the industry for a low cost apparatus that utilizes the conventional clampband design, but also allows a gentle release of the elements held by the clampband. An apparatus that allows a reduction or substantial elimination of the source of the shock created by the release of constrained or potential energy stored in clampbands would substantially decrease the shock experienced by the elements joined by the clampband upon clampband separation and, therefore, reduce the risk of damage to sensitive equipment or electronics carried by the elements. In addition, reducing or substantially eliminating the constrained or potential energy stored in the clampband that creates low frequency vibrations in the elements upon clampband separation is desirable in order to reduce the risk of damage to sensitive equipment carried by the elements, such that elements with less protection may be utilized in particular applications, which can decrease the cost of the elements.